There’s a profile of Peter Dinklage due to his role in an upcoming comedic film. In it, he discusses his views on playing roles which focus too much on the character being a dwarf. He adds that there are certainly great roles written for dwarves, and it seems that Tyrion Lannister may have come up in that context:

‘It would entail me being lazy, and I’m not interested in that,” he says. “It just becomes uninteresting for me and I think it becomes uninteresting for an audience.” Having said that, he notes: “There are great roles that are written for dwarves.”

‘That would include his current project, a planned HBO series called Game of Thrones, based on the popular fantasy series A Song of Ice and Fire by George R. R. Martin. Dinklage plays the diminutive Tyrion Lannister in the pilot episode.’